1. Field of the Invention
This invention relates to a tire building drum of the radial collapsing type, for use in the manufacture of pneumatic tires primarily for road vehicles.
2. Description of the Prior Art
Tire building drums have a cylindrical body, rotatable about its axis and upon the cylindrical surface of which tire carcasses are assembled. In order to facilitate removal of constructed carcasses from the drum the cylindrical body of the drum is collapsible. Tire building drums generally fall into either of two categories known respectively as rotary (or inertia) collapse drums and radial collapse drums.
The cylindrical body of a tire building drum is formed in a number of axially extending segments and in the rotary collapse drum the segments are connected by means of pivoting links to a hub, pivoting of the links generating collapsing or expanding movement of the segments. In the radial collapse drum the segments are supported on radially extending pillars or slides, and during collapsing and expanding movement of the segments the segments are moved radially, by operation of a collapsing mechanism with respect to the rotational axis of the drum.
Both types of drum have a main shaft by means of which the drum is mounted, and through which rotational movement is transmitted to the drum. In the rotary collapse drum the arrangement of pivoting links lends itself readily to the provision of a hollow outer shaft through which the main shaft passes, the hollow outer shaft being coupled to the collapsing mechanism of the drum so that relative rotation between the outer hollow shaft and the main shaft operates the collapsing mechanism either to collapse, or expand the segments of the drum. In the radial collapse drum however the internal structure necessitates, in order to achieve a firm and accurate support of the segments, a hub having parts adjacent each axial end of the segments by means of which the segments are supported. The collapsing mechanism is disposed between the two hub portions, and in order to transmit movement to the collapsing mechanism in the radial collapse drum the main shaft and hub are hollow and receive an inner shaft which is connected to the collapsing mechanism by way of a radial aperture in the wall of the hub. Such a known construction is illustrated in U.S. Pat. No. 3,779,835.
Currently preferred tire manufacturing techniques are served best by radial collapse type drums, particularly where the manufacturing technique involves the use of partly preformed carcases, that is to say bands of plys, which must be threaded over the collapsed drum, the drum then being expanded within the partially preformed carcass. However, while the radial collapse tire of drum is now preferred for many tire building applications, the majority of tire building installations were designed for use with rotary collapse drums, and unless extensive modification of the apparatus for supporting and driving the drum is undertaken the radial collapse drum cannot be substituted for the rotary collapse drum because of the very significant difference in the manner in which drive is transmitted to the collapsing mechanism of the drum.